Direct current dynamoelectric machines

ABSTRACT

A direct current dynamoelectric machine has poles in the usual way, but each pole has a first portion formed from steel and a second portion formed from ferrite material. The steel has a lower reluctance than the ferrite material, but in use the flux density is increased by armature reaction in the vicinity of the steel portion, and reduced by armature reaction in the vicinity of the ferrite portion, so that the required characteristics of the machine are obtained with a saving in material. The same effect, utilizing the armature reaction to increase flux density beneath a pole part which has a lower reluctance than the other part of the pole, can be achieved in other ways.

United States Patent [72] Inventor JdmGodfrey Wilson West SuttonColdlield, England [21 1 App]. No. 847,249 [22] Filed Aug. 4,1969 [45]Patented July 20, 1971 [73] Assignee Joseph Lucas (Industries) LimitedBirmingham, England [32] Priority Aug. 16, 1968 [33] Great Britain [31 139,324/68 [S4] DIRECT CURRENT DYNAh/IOELECT RIC Primary Examiner-Milton0. Hirshfi'eld Assistant Examiner-R Skudy Attorney-Holman & SternABSTRACT: A direct current dynamoelectric machine has poles in the usualway, but each pole has a first portion formed from steel and a secondportion formed from ferrite material. The steel has a lower reluctancethan the ferrite material, but in use the flux density is increased byarmature reaction in the vicinity of the steel portion, and reduced byarmature reaction in the vicinity of the ferrite portion, so that therequired characteristics of the machine are obtained with a saving inmaterial. The same effect, utilizing the armature reaction to increaseflux density beneath a pole part which has a lower reluctance than theother part of the pole, can be achieved in other ways.

PATENTEU JUL20 9n SHEET 2 OF 2 EYS M M W WW9 U DIRECT CURRENTDYNAMOELECTRIC MACHINES This invention relates to direct currentdynamoelectric machines.

The invention resides in a direct current dynamoelectric machine inwhich at least a part of each pole of the machine beneath which the fluxdensity is increased by armature reaction has a lower reluctance thanthe part of each pole beneath which the flux'density is reduced byarmature reaction.

In the case of a motor, the leading edge of each polc has the lowerreluctance, whilst in the case of a generator the trailing edge of eachpole has the lower reluctance.

In the accompanying drawings, FIGS. 1 to 6 respectively are sectionalviews illustrating six examples of the invention. For the purposes ofthe description it will be assumed that each of the examples is a motor.

Referring to FIG. 1, there is shown a two-pole machine in which eachpole comprises two parts ll, 12, the parts I l being fonned from steel,and the parts 12 being ferrite magnets. The parts 11 may be wound. Therotor (indicated in dotted lines at 10) rotates in a clockwisedirection, so that the parts 12 are on the trailing edge, The reluctanceof the parts 11 is considerably lower than the reluctance of the parts12-, but the armature reaction increases the flux density beneath theparts 11 and reduces it beneath the parts 12, the design being such thata substantially even flux distribution is obtained. The design requiresconsiderably less ferrite material than if the entire pole was formedfrom ferrite, and as compared with a wound machine, will requireconsiderably fewer windings.

FIG. 2 is similar to FIG. 1 in that each of the poles includes a ferritemagnet 12 and a steel part 1 l. The magnets 11 are held in position bybolts 13, and the parts 12 are held in position by springs 14 urging theparts 12 against their associated magnets I 1.

FIG. 3 shows another two-pole machine in which each pole comprises twoportions as in FIGS. 1 and 2. However, in this case the high-reluctanceportion is formed by a relatively thick ferrite magnet 15 having securedthereto a steel pole piece 16,

and a relatively low-reluctance portion comprising a thinner ferritemagnet 17 and associated steel pole piece 18.

In FIG. 4 the stator is of noncircular cross section, and both poles 19are formed entirely from ferrite. However, it will be seen that thepoles 19 are shaped to present a relatively thin portion on the leadingedge and a relatively thick portion of the trailing edge. In FIG. 4 thedirection of rotation of the rotor is clockwise, as it is in FIG. 5which differs from FIG. 4 in that each pole is formed from onerelatively thick ferrite magnet 21 and a second relatively thin ferritemagnet 22.

In FIG. 6, magnets 2] equivalent to those in FIG. 5 are used, but inplace of the magnet 22 the actual stator is shaped as indicated at 23 toconstitute the low-reluctance portion of each pole.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

I. A direct current dynamoelectric machine having a plurality of poles,and a rotor rotating beneath said poles and producing a conventionalarmature reaction, each pole having a first pole part beneath which theflux density is increased by armature reaction and a second pole partbeneath which the flux density is reduced by armature reaction, saidpole parts being circumferentially disposed, and wherein each of saidfirst pole parts is constructed with a lower reluctance than each ofsaid second pole parts.

2. A machine as claimed in claim 1 in which each pole has 7 two partsformed respectively from steel and ferrite, the steel part constitutingthe first pole part of each pole.

3. A machine as claimed in claim I in which the first pole part of eachpole is formed by a ferrite magnet and associated steel pole piece, andthe second pole part of each pole is formed by a thicker ferrite magnetand associated steel pole |ece. p 4. A machine as claimed in claim 1 inwhich each pole is formed entirely from ferrite material, the thicknessof the ferrite material varying from a maximum to a minimum to providethe first and second pole parts of each pole.

5. A machine as claimed in claim 2 in which the steel part isconstituted by the stator.

1. A direct current dynamoelectric machine having a plurality of poles,and a rotor rotating beneath said poles and producing a conventionalarmature reaction, each pole having a first pole part beneath which theflux density is increased by armature reaction and a second pole partbeneath which the flux density is reduced by armature reaction, saidpole parts being circumferentially disposed, and wherein each of saidfirst pole parts is constructed with a lower reluctance than each ofsaid second pole parts.
 2. A machine as claimed in claim 1 in which eachpole has two parts formed respectively from steel and ferrite, the steelpart constituting the first pole part of each pole.
 3. A machine asclaimed in claim 1 in which the first pole part of each pole is formedby a ferrite magnet and associated steel pole piece, and the second polepart of each pole is formed by a thicker ferrite magnet and associatedsteel pole piece.
 4. A machine as claimed in claim 1 in which each poleis formed entirely from ferrite material, the thickness of the ferritematerial varying from a maximum to a minimum to provide the first andsecond pole parts of each pole.
 5. A machine as claimed in claim 2 inwhich the steel part is constituted by the stator.